The invention relates to a method for processing vegetable oil miscella, an apparatus for processing vegetable oil miscella, a method for conditioning a polymeric microfiltration membrane for selective removal of phospholipids from vegetable oil miscella, a membrane for selective removal of phospholipids from vegetable oil miscella, and a lecithin product.
Edible vegetable oils are generally obtained by processing oil seeds. Crude vegetable oils can be obtained from vegetable seeds by solvent extraction. Hexane is the most commonly used extraction solvent. The crude vegetable oils generally contain neutral triglycerides and a host of natural contaminants including phosphotides, sulphurous compounds, free fatty acids, carbohydrates, peptides, oxidized lipids, traces of lower aldehydes and ketones, glycosides of sterols and terpenes, and diverse types of color bodies or dyestuffs. These contaminants are removed from the crude vegetable oils in the course of refining in order to render the vegetable oils palatable.
The recovery of soybean oil from soybeans is particularly desirable. A technique for recovering soybean oil includes several processing steps. The soybean is dehulled and crude soybean oil is extracted with hexane. The extractant (miscella), which includes hexane and crude soybean oil, is further processing to recover palatable soybean oil. The hexane is evaporated from the miscella and the resulting crude soybean oil is degummed. Degumming, as used in conventional processes, refers to the removal of phosphatides and other gums from the oil by adding water and/or acid thereto and centrifuging. The recovered oil can be further refined with water and alkaline (such as NaOH) and centrifuged to remove the fatty acids and gums. The oil resulting from the alkaline refining step can then be bleached to remove color bodies, hydrogenated to render the oils more stable, and deodorized. The techniques of degumming, alkaline refining, bleaching, hydrogenating, and deodorizing are well known in the art. It should be appreciated that each separation step, and particularly centrifuging, results in loss of oil. The recovered gum concentrate from the conventional degumming process can be dried, if desired, and bleached to produce a commercial soybean lecithin.
Lecithin is used as an emulsifying agent, a dispersing agent, wetting agent, a penetrating agent, and an anti-oxidant. In addition, lecithin is used in food products, paints, inks, petroleum products, soaps, cosmetics and lubricants. Commercial lecithin is a mixture of phosphatides. Typically, commercially available lecithin includes about 62 wt. % acetone insoluble phosphatides.
Numerous prior art references describe techniques for obtaining vegetable oils by application of membrane technology. For example, U.S. Pat. No. 4,093,540 to Sen Gupta describes refining crude glyceride oils by contacting a composition of glyceride oils and organic solvent under pressure with a semi-permeable ultrafiltration membrane to separate constituents of different molecular weight into retentate and permeate fractions, and contacting the composition or at least one of the fractions with a metal oxide or metalloid oxide adsorbent in a column containing the adsorbent. Additional references which describe the use of membrane technology for separating phospholipids from crude vegetable oils include: U.S. Pat. No. 4,414,157 to Iwama et al.; U.S. Pat. No. 4,533,501 to Sen Gupta; Raman et al., xe2x80x9cMembrane Technologyxe2x80x9d, Oils and Fats International, Vol. 10, No. 6, 1994, pages. 28-40; Ziegelitz, xe2x80x9cLecithin Processing Possibilitiesxe2x80x9d, Inform, Vol. 6, No. 11, November 1995, pages. 1224-1213; Ondrey et al., xe2x80x9cThe Skinny On Oils and Fatsxe2x80x9d, Chemical Engineering, October 1997, pages. 34-39; Pioch et al., xe2x80x9cTowards An Efficient Membrane Based Vegetable Oils Refiningxe2x80x9d, Industrial Crops and Products, 7 (1998) pages 83-89; Koseoglu et al., xe2x80x9cMembrane Applications and Research In The Edible Oil Industry: And Assessment, JAOCS, Vol. 67, No. 4 (April 1990), pages 239-249.
A method for processing vegetable oil miscella is provided by the present invention. The vegetable oil miscella can be processed into desirable products including vegetable oil and concentrated lecithin.
The method for processing vegetable oil miscella includes a step of feeding vegetable oil miscella to a separation membrane for recovery of a permeate stream and a retentate stream. The separation membrane is provided for removing phospholipids. The recovered permeate stream has a decreased concentration of phospholipids compared with the concentration of phospholipids provided in the miscella. In addition, the retentate stream has an increased concentration of phospholipids compared with the concentration of phospholipids provided in the miscella.
In the context of the present invention, the permeate stream is the stream which flows through the membrane, and the retentate stream is the stream which does not flow through the membrane. The vegetable oil miscella includes extraction solvent and crude vegetable oils containing phospholipids. The vegetable oil miscella can be characterized as raw miscella when it is obtained from refers to as extractant from an extraction process for the recovery of vegetable oils and has not been clarified for the removal of solids. The vegetable oil miscella can be characterized as clarified miscella when it has be treated for the removal of solids.
The separation membrane refers to the membrane which provides for the separation of phospholipids from vegetable oil. The separation membrane can be referred to as the phospholipids separation membrane. In general, the separation membrane can be provided by modifying a membrane having a pore size of between about 0.05xcexc and about 3xcexc, and more preferably between about 0.1xcexc and about 2xcexc. The modification refers to conditioning which involves treating the membrane with a solvent or solvent system that allows the membrane to be used for separating phospholipids from vegetable oil. The polymeric membrane which is to be conditioned is generally a membrane provided in an aqueous medium. In order to use the membrane with miscella, the membrane can be conditioned.
The vegetable oil miscella preferably contains between about 45 percent by weight and about 90 percent by weight extraction solvent, and more preferably between about 70 percent by weight and about 80 percent by weight extraction solvent. A preferred extraction solvent includes hexane. The permeate stream preferably includes less than 0.6 weight percent phospholipids, more preferably less than about 0.15 weight percent phospholipids, and even more preferably less than about 0.015 weight percent phospholipids.
The vegetable oil miscella which is obtained from an extraction operation generally contains a relatively high level of solids which, if not removed from the miscella, will relatively quickly clog the phospholipids separation membrane. Accordingly, it is desirable to provide a prefilter system for removing the solids in the miscella. The prefilter system can include one or more filters in series to provide reduction of the solids content in the miscella. The resulting miscella having a reduced solids content can be referred to as clarified miscella. In general, the filters used to remove solids from the miscella have an average pore size in the range of about 0.05xcexc and about 100xcexc. It is generally advantageous to provide a series of filters having decreasing pore size so that upstream filters remove the relatively large solids and the downstream filters remove the smaller solids. The filters which can be used in the prefilter system need not include conditioned membranes. The filters used in the prefilter system can include stainless steel filters. In addition, the filters can be dead end filters and/or feed and bleed filters. Furthermore, the prefilter system can be practiced batch or continuous. In addition, it will be appreciated that although the filters used for separating phospholipids from vegetable oil are described in the context of continuous operation, they can be used in batch.
The phospholipids separation filter referred to above can be referred to as the first phospholipids separation filter. The retentate stream from the first phospholipids separation filter can be further processed in a second phospholipids separation filter for the separation of phospholipids from vegetable oil. The feed to the second phospholipids separation filter preferably includes a combination of the retentate stream from the first phospholipids separation filter and additional solvent. It is generally desirable to provide the additional solvent to help drive vegetable oil through the membrane provided in the second phospholipids separation filter. The resulting retentate stream can be processed into a lecithin product containing between about 50 wt. % and about 85 wt. % phospholipids. Preferably, the lecithin product includes between about 72 wt. % and about 85 wt. % phospholipids. In addition, the permeate stream from the second phospholipids separation filter can be recycled by combining it with the clarified miscella.
The permeate stream from the first phospholipids separation filter can be fed to a third phospholipids separation filter for the separation of phospholipids from vegetable oil. Although the permeate stream from the first phospholipids separation filter may be a commercially acceptable vegetable oil product, it may be desirable to further remove phospholipids. Accordingly, the permeate stream from the third phospholipids separation filter can provide vegetable oil having a phospholipids content of less than 7 ppm. In addition, the retentate stream from the third phospholipids separation filter can be recycled by combining it with the clarified miscella.
An apparatus for processing vegetable oil miscella is provided by the invention. The apparatus includes at least the first phospholipids separation filter, including the separation membrane. The apparatus can additionally include any of the second phospholipids separation filter, the third phospholipids separation filter, and the prefilter system, and any of the conduits or lines connecting these various components.
A method for conditioning a membrane is provided by the invention. The method includes providing a polymeric microfiltration membrane characterized as having an average pore size in the range of about 0.05xcexc to about 3xcexc, and more preferably in the range of about 0.1xcexc and about 2xcexc, and more preferably between about 0.2xcexc and about 0.5xcexc. Preferably, the polymeric microfiltration membrane comprises polyacrylonitrile, polysulfone, polyamide, or polyimide. The polymeric microfiltration membrane can be conditioned by treating the membrane with an intermediate solvent, and then treating the membrane with an extraction solvent. A preferred embodiment of the invention includes treating the membrane with a mixture of intermediate solvent and extraction solvent between the steps of treating the membrane with an intermediate solvent and treating the membrane with raw miscella. The conditioned polymeric membrane can be used as the separation membrane in any of the first, second, and third phospholipids separation filters. In addition, the conditioned membrane can be used in the prefilter system, if desired. Preferably, the conditioned membrane used in the third phospholipids separation filter is tighter than the conditioned filter used in the first phospholipids separation filter.
Another technique for conditioning the membrane includes treating the membrane with raw miscella. In general, this technique can include a first step of treating the membrane with the solvent provided in the raw miscella, and then treating the membrane with the raw miscella. The steps of treating generally include treating for at least about 10 minutes, and more preferably at least about 20 minutes. In most situations, it is believed that the treating can occur for about one hour. Although longer treating times can be provided, it should be understood that longer treating times result in a down-time or delay in the separation operation.
The steps of treating the membrane with solvent are conducted for a period of time which is sufficient to provide the desired level of conditioning. In most cases, it is expected that the treatment will include flushing and/or soaking for at least about one-half hour. For convenience, it may be desirable to allow the membrane to soak in the particular solvent over night or for a period of up to about 24 hours. It should be understood that longer soaking times are permitted.
The treatment with the intermediate solvent is advantageous to reduce the likelihood of shocking or harming the membrane when treated with the extraction solvent or the miscella. Exemplary intermediate solvents include alcohols and acetone. Preferably, the intermediate solvent is one which is miscible with the extraction solvent. In the case of using hexane as the extraction solvent, the intermediate solvent is preferably ethanol, propanol or a mixture of ethanol and propanol.
A conditioned polymeric microfiltration membrane is provided by the invention. The conditioned membrane can be characterized as a membrane resulting from the steps of conditioning. In addition, the conditioned membrane can be characterized in terms of its performance. For example, a soybean oil miscella can be providing containing 25 percent by weight crude soybean oil and 75 percent by weight hexane, and containing a phosphorous level of about 5,000 ppm in the crude oil. By feeding the miscella to the membrane at a transmembrane pressure of about 150 psi, it is expected that the membrane will provide a steady state permeate at a flux of greater than about 65 l/hr m2 and a phosphorous level of less than about 50 ppm. Preferably, the phosphorous level will be less than about 25 ppm. More preferably, the flux will be greater than about 80 l/hr m2.
A lecithin product composition is provided according to the invention. The lecithin product can be prepared by processing through the phospholipids separation filter according to the invention, and includes a phospholipids concentration of between about 50 wt. % and about 85 wt. % after volatilization to remove solvent. Preferably, the lecithin has a phospholipids concentration of between about 72 wt. % and about 85 wt. %, and more preferably between about 75 wt. % and about 85 wt. %.